Can't make updates from admin

I'm new to Zen Cart and could use some help. I seem to be unable to make changes from the admin. For example, if I try to make changes to the ez-pages, tax rates or store configuration it allows me to go through all the steps but when I click "update" it directs me back to the main admin page but does not accept the changes. The only area that seems to work are the product pages- I can make changes to the product page but nothing else works. This started a few days ago - before that everything was working fine.

Does anyone have any ideas of what might be causing this and how I can fix this? Any help would be greatly appreciated.

Run,
What version of Zen Cart are you using?
What third party modules had you incorporated within your site?

I am using version 1.3.8a and the only third party module that I added is Image Handler 2. I should probably mention that I hired someone to create a custom template but when they uploaded the template everything was working fine and since the template was uploaded, the only changes that I have made have been through the admin and some changes to the css file.

runawayd:

I am using version 1.3.8a

Re-upload the june2009 security patches, or more specifically, double check that the file /admin/includes/functions/html_output.php was correctly installed (it needs to overwrite the original file).

Cheers
Rod

Thanks Rod. That seemed to do the trick. Thank you so much for your input. I really appreciate it.